The goal of this research is to elucidate the ionic mechanisms responsible for the action potential in cardiac muscle. To this end an attempt was made to apply the double sucrose-gap voltage clamp technique to frog atrial muscle, but recent experiments indicate that the voltage clamp of a multicellular preparation is not very feasible. In light of these recent experiments, we are presently developing techniques which will allow the investigation of the electrophysiological properties of isolated adult cardiac cells. The response of the isolated cell to various drugs will be compared to the response of a cell in an intact piece of cardiac muscle in order to assess the similarities and differences which might exist between the behavior of a cardiac cell isolated from neighboring cells and the behavior of a cardiac cell in intact tissue. By these studies, information can be obtained which will further our understanding of the excitatory process in cardiac cells.